1. Field
The present disclosure relates to light emitting devices, and more particularly, to semiconductor light emitting devices having a phosphor layer.
2. Background
Light emitting diodes (LEDs) are attractive candidates for replacing conventional light sources, such as incandescent lamps and fluorescent light sources. LEDs have substantially higher light conversion efficiencies than incandescent lamps and longer lifetimes than both types of conventional light sources. In addition, some types of LEDs now have higher conversion efficiencies than fluorescent light sources and still higher conversion efficiencies have been demonstrated in the laboratory. Furthermore, LEDs require lower voltages than fluorescent lamps, and therefore, are better suited for applications in which the light source must be powered from a low-voltage source, such as a battery or an internal computer DC power source.
Unfortunately, LEDs produce light in a relatively narrow spectrum band. To replace conventional lighting sources, LEDs that generate light that appears to be “white” to the human observer are required. A light source that appears to be white and that has a conversion efficiency comparable to that of fluorescent light sources can be constructed from a blue light emitting semiconductor covered with a layer of phosphor that converts a portion of the blue light to yellow light. If the ratio of blue to yellow light is chosen correctly, the resultant light source appears white to a human observer. In applications requiring high power illumination, however, the phosphor layer may overheat because in the conversion process it itself generates heat. The heat, if not sufficiently dissipated, may cause degradation of the phosphor layer, decreasing the device's performance and life-span.
To improve the efficiency of light output as well as the color consistency, some contemporary devices are designed with a separately manufactured phosphor layer mounted further away from the light emitting semiconductor. This approach, however, creates additional problems. The phosphor layer may heat up significantly due to the light conversion process itself, resulting in decreased efficiency and degradation. Hence, such a design does not effectively address the heat dissipation issue as it does not provide any means for dissipating the heat away from the phosphor layer.
Accordingly, although contemporary LEDs have proven generally suitable for their intended purposes, they possess inherent deficiencies which detract from their overall effectiveness and desirability. As such, there exists a need for small, high-power “white light” LEDs with a system for dissipating heat from the phosphor layer.